moon

moon.c

#include <stddef.h>
#include <stdint.h>

size_t moon_phase_index(float day) {
    static const float BOUNDS[7] = {3.69, 7.38, 11.07, 14.76, 18.45, 22.14, 25.83};
    uint_fast8_t a = 0;

    if (day >= BOUNDS[a + 3]) a = a + 4;
    if (day >= BOUNDS[a + 1]) a = a + 2;
    if (day >= BOUNDS[a + 0]) a = a + 1;
    return a;
}

#include <stdio.h>
int main() {
    for (float t = 0.0; t < 30; t += 1.0) {
        printf("%2.1f -> %lu\n", t, moon_phase_index(t));
    }
    return 0;
}

moon.py

from typing import NamedTuple
from random import random


class Phase(NamedTuple):
    name: str


PHASES = [
    Phase("New Moon"),
    Phase("Waxing Cresent"),
    Phase("First Quarter"),
    Phase("Waxing Gibbous"),
    Phase("Full Moon"),
    Phase("Waning Gibbous"),
    Phase("Third Quarter"),
    Phase("Waning Crescent"),
]


def moon_phase_index(day: float) -> int:
    PHASE_UPPER_BOUNDS = [3.69, 7.38, 11.07, 14.76, 18.45, 22.14, 25.83]
    a = 0
    a = [a, a + 4][day >= PHASE_UPPER_BOUNDS[a + 3]]
    a = [a, a + 2][day >= PHASE_UPPER_BOUNDS[a + 1]]
    return [a, a + 1][day >= PHASE_UPPER_BOUNDS[a]]


for t in range(30):
    i = moon_phase_index(0.0 + t)
    print(t, i, PHASES[i].name)